The Influence of Aluminum on Iron Oxides. XV. Al-for-Fe Substitution in Synthetic Lepidocrocite

Abstract

Abstract--Lepidocrocite samples, 7-FeOOH, containing 0-10 mole % Al-for-Fe substitution were synthesized at 15~ and pH 8 by oxidizing mixed FeCI2-A1C13 solutions. The unit-cell parameters a, b. and c were measured from step-counted X-ray powder diffractograms using seven lines and Si as an internal standard. With increasing Al substitution from 0 to 10 mole % the unit-cell edge lengths a, b, and c decreased regularly by 0.3, 0.8, and 0.6%, respectively. Furthermore, the crystals became smaller, but gained in thermal stability. Decrease in crystal size parallel to the y axis led to a significant increase of the OH-stretch vibration and a decrease of the out-of-plane OH-bending vibration due to a weakening of the hydrogen bond between the zig-zag layers in the structure.

57Fe Mössbauer Effect Study of Al-Substituted Lepidocrocites

“…The significantly lower values as compared to the results obtained for the present samples, are in the authors' opinion a strong indication that the A1 species are incorporated in the structure of these latter lepidocrocites, at least for AI/ (A1 + Fe) ratios of up to 0.10 tool/tool in the initial solution. This finding supports the observed diminution of the unit cell (Schwertmann and Wolska 1990).…”

“…For low AI contents, including x = 0.0, these plates exhibit strongly serrated edges. This typical morphology, however, becomes less expressed with increasing AI content (Schwertmann and Wolska 1990) and for x -> 0.05 the edges are rounded-off.…”

“…Some years ago, Schwertmann and Wolska (1990) concluded from precise X-ray diffraction (XRD) analyses that lepidocrocite, ~/-FeOOH, can incorporate A1 into its structure, at least up to A1/(A1 + Fe) concentrations of 0.1 mol/mol. The presence of A1 cations was observed resulting in small, downward shifts in the unit-cell edge lengths and volume of the host lepidocrocite.…”

“…The latter one has a considerably higher degree of crystallization. EXPERIMENTAL Samples used were prepared by oxidation of FeCI2/ AI(NO3) 3 solutions with Al-to-(A1 + Fe) fractions C~ of 0.0025, 0.01, 0.025, 0.05, 0.075, 0.10 and 0.15 mol/ mol, and characterized by Schwertmann and Wolska (1990). The AI/(A1 + Fe) ratios, x, in the final solid products, designated as ~/-Fe~_xAlxOOH, were determined analytically from the above prepared samples as 0.0047, 0.0141, 0.0265, 0.0598, 0.0785, 0.1031 and 0.141 respectively, and are somewhat different from the initial solution compositions, especially for the lower ones.…”

The application of chromium substituted magnetite as heterogeneous Fenton catalyst for the degradation of aqueous cationic and anionic dyes

“…The overall density of surface hydroxyl is related to the crystal structure and extent of the development of different crystal faces [37]. From XANES results, the incorporation of chromium results in a slight distortion of the magnetite lattice, leads to the increase in surface hydroxyl amount [38]. (Fig.…”